1. Field of the Invention
The present invention relates to a dual mode mobile phone (xe2x80x9cmobilexe2x80x9d) which transmits and receives radio frequency (RF) signals during normal operation using frequency division duplexing, and operates as a two-way radio during a supplemental operating mode.
2. Description of Prior Art
Consumer demand and competition in the wireless communications industry has driven a rapid evolution in cellular phone technology. Analog mobiles introduced in the early 1980s are being replaced by digital technology which offers enhanced quality, security, and efficient spectrum use.
Using PCS (personal communication services) devices as an example, service providers are now able to attract cellular customers by offering an expanded variety of services, such as voicemail, short message service, and personal call management (i.e., providing a single telephone number for a user""s home, mobile, and office). Although it is desirable to offer these and other services to cellular customers, it is also desirable to minimize the effect of such services on the cost, size, and convenience of the mobile.
The present invention adds two-way radio functionality to a frequency division duplex mobile in an efficient manner. The user of the dual mode mobile according to the present invention switches between a normal operating mode, for cellular service, and a two-way radio mode (also referred to herein as xe2x80x9cwalkie-talkie,xe2x80x9d or xe2x80x9cW-Txe2x80x9d mode) which enables short-range, low-power communication with similarly equipped phones without using the service provider""s cellular infrastructure (i.e., without transmitting or receiving to/from a cellular network base station). In W-T mode, the dual mode mobile transmits and receives at frequencies between the mobile""s normal transmit and receive frequency bands. By utilizing these in-between frequencies, numerous transmitter/receiver components are used for both normal cellular communication and during W-T mode, thereby allowing design efficiencies to minimize the cost and size of the dual mode mobile.